In a letter today, Rep. Darrell Issa (R-CA), Chairman of the House Oversight Committee, criticized the ATF for not complying with a subpoena issued last month and turning over documents related to Project Gunrunner and Operation Fast and Furious.

"If you do not comply with the subpoena, the Committee will be forced to commence contempt proceedings," Rep. Issa wrote to Kenneth E. Melson, Acting Director of the Bureau of Alcohol, Tobacco, Firearms, and Explosives.

The subpoena deals with allegations that ATF knowingly allowed thousands of guns to be smuggled into the hands of Mexican drug cartels. These allegations were first made public in a series of reports by CBS News investigative correspondent Sharyl Attkisson.

Issa wrote he was "disappointed that you have failed to produce any documents that would meet your legal obligations by the subpoena's April 13th deadline." Issa said the letter he received from Assistant Attorney General Ronald Weich did not assert a claim of executive privilege - rather "the department's 'on-going criminal investigations.'" Issa said these "vague assertations are not a valid basis for your decision to withhold documents."

Issa attached several documents obtained by the Committee that indicate, "not only that the Department and ATF were aware that straw purchases were consistently and illegally buying assault rifles and other weapons, but that they also failed to prevent their disappearance."